Enhanced recovery of argon from cryogenic air separation cycles

Abstract

The present invention relates to an improvement for the production of argon from cryogenic air separation processes. In particular, the improvement provides a better method of thermally linking the top of the crude argon column with the low pressure column. In the improvement, the argon-rich, overhead vapor from the top of the crude argon column is condensed in a boiler/condenser by indirect heat exchange against liquid descending the low pressure column; a portion of the condensed argon-rich, overhead vapor is returned to the top of the crude argon column to provide reflux. The most suitable location for such boiler/condenser is as an intermediate boiler/condenser in the low pressure column, particularly, the section of the low pressure column bounded by the feed point of the crude liquid oxygen from the bottom of the high pressure column and the vapor feed draw line for the crude argon column wherein an adequate temperature difference exists between the descending liquid and the condensing argon.

We claim: 
     
       1. In a cryogenic air distillation process producing argon using a multiple column distillation system comprising a high pressure column, a low pressure column and a crude argon column; wherein feed air is compressed, cooled and at least a portion thereof is fed to the high pressure column; wherein in the high pressure, the compressed, cooled feed air is rectified into a crude liquid oxygen bottoms and a high pressure overhead; wherein the crude liquid oxygen bottoms is fed to the low pressure column; wherein in the low pressure column, the crude liquid oxygen is distilled into a liquid oxygen bottoms and a gaseous nitrogen overhead; wherein the low pressure column and the high pressure column are thermally linked such that at least a portion of the high pressure nitrogen overhead is condensed in a reboiler/condenser against vaporizing liquid oxygen bottoms; wherein an argon containing gaseous side stream is removed from a lower intermediate location of the low pressure column and fed at essentially the same pressure to the crude argon column; wherein in the crude argon column, the argon containing gaseous side stream is rectified into an argon-rich vapor overhead and an argon-lean bottoms liquid, and the argon-lean bottoms liquid is returned to the low pressure column; the improvement for increasing argon recovery comprises condensing at least a portion of the argon-rich vapor overhead from the crude argon column by heat exchange in a boiler/condenser against at least a portion of liquid descending the low pressure column selected from a location of the low pressure column between the feed point of the crude liquid oxygen from the bottom of the high pressure column and the removal point for the argon containing gaseous side stream for the crude argon column wherein an adequate temperature differences exists between the descending liquid and the condensation argon, thereby at least partially vaporizing said liquid portion; and returning at least a portion of the condensed argon to a top of the crude argon column to provide liquid reflux. 
     
     
       2. The process of claim 1 which further comprises using at least a portion of said at least partially vaporized liquid portion to provide reflux to the low pressure column. 
     
     
       3. The process of claim 2 wherein said boiler/condenser for the condensation of at least a portion of the argon-rich vapor overhead of the crude argon column is located internal to the low pressure column. 
     
     
       4. The process of claim 1 wherein said boilder/condenser for the condensation of at least a portion of the argon-rich vapor overhead of the crude argon column is located internal to the low pressure column. 
     
     
       5. The process of claim 1, which further comprises condensing a portion of the vapor ascending the intermediate section of the crude argon column by indirect heat exchanger in a second boiler/condenser against liquid descending the low pressure column bounded by the location of the liquid used to condense at least a portion of the argon-rich vapor overhead and the removal point for the argon containing gaseous side stream for the crude argon column and using said condensed portion as intermediate reflux for the crude argon column. 
     
     
       6. The process of claim 3, which further comprises condensing a portion of the vapor ascending the intermediate section of the crude argon column by indirect heat exchanger in a second boiler/condenser against liquid descending the low pressure column bounded by the location of the liquid used to condense at least a portion of the argon-rich vapor overhead and the removal point for the argon containing gaseous side stream for the crude argon column and using said condensed portion as intermediate reflux for the crude argon column; wherein said second boiler/condenser is located internal to the low pressure column.